1. Field of the Invention
This invention relates to a plant growing device, more particularly to a plant growing device of the type that includes an envelope containing a plant growing medium.
2. Description of the Related Art
Various envelopes have been suggested in the art for the plant growing device of the above-mentioned type. For example, U.S. Pat. No. 6,415,548 discloses an envelope that is made from a sheet material and that is formed with slit pre-markings operable for drainage and for accommodating seeds.
U.S. Pat. No. 5,761,847 discloses a covering material for growing plants, which is made of a water-impermeable resin sheet of woven or nonwoven fabric having a basis weight of 20 to 100 g/m.sup.2, a visible-ray reflectance of more than 60%, and an air-permeability of 10 to 200 sec/100 cc. The resin sheet is formed from fibers, such as flash-spinning high density polyethylene fibers. This patent further discloses that, if the basis weight is less than 20 g/m.sup.2, the sheet will be too week to be used as the covering material for filling a substrate. On the contrary, if the basis weight exceeds 100 g/m.sup.2, a required air-permeability will not be provided. Accordingly, the basis weight is an important factor to optimize air-permeability and strength of the covering material.